Commonplace books (or commonplaces) are a way to compile knowledge, usually by writing information into books. They have been kept from antiquity, and were kept particularly during the Renaissance and in the nineteenth century. Such books are similar to scrapbooks filled with items of many kinds: sententiae, notes, proverbs, adages, aphorisms, maxims, quotes, letters, poems, tables of weights and measures, prayers, legal formulas, and recipes.
Arguably this entire knowledge base is a commonplace book. But this section is specifically for scribbles and whatnot, things that don’t fit elsewhere.